A known seat for a vehicle employs a balloon body (an airbag) that swells by being filled with air. For example, a configuration in which a so-called balloon-type child seat is retracted in a retracting chamber provided inside a seatback or a seat cushion is disclosed in U.S. Pat. No. 7,413,249 (hereinafter referred to as Patent reference 1). In the conventional example, the child seat which swells within the retracting chamber is configured to be deployed on the seat by pushing to open a lid portion which is provided at a backrest surface of the seatback or at a seat surface of the seat cushion.
However, the child seat which is formed by the aforementioned conventional technology is configured to support a load of an occupant in a seat width direction only by the balloon body. Thus, there is an issue in which support strength in the seat width direction is difficult to be enhanced. Accordingly, favorable seat support performance may not be secured, and there still is a room for improvement.
A need thus exists for a seat device for a vehicle which is not susceptible to the drawback mentioned above.